3.9L LZ9 engine internal upgrade & performance?

[Superdave]

Hmm. From looking at the CR calc, that would be a .2" overbore on an LX9... LOL. So I'm assuming you can't really use the LZ9 heads on anything older than the gen4s... Darn.

iirc there were other changes in the block that made that head swap not work. Something about coolant ports not lining up...

[Joseph Upson]

iirc there were other changes in the block that made that head swap not work. Something about coolant ports not lining up...

The heads are left and right and their deck surface coolant passages differ as you move from the front end of the head to the rear. They also have a larger surface and would overhang on the non VVT motors deck surface towards the sides. They are made very well and after looking at mine in consideration of some port work I lost motivation as the area around the valve guide in the bowl is pretty neat as well as the overall port, so aside from widening the passage beneath the valve there probably isn't much to gain.

[IsaacHayes]

^^ Cool, so you can get a 3900 and leave it alone and just slap a turbo on Of course that means less potential if it's already close to optimal from the factory. I'm really curious to see the #s from a turbo 3900.

[SappySE107]

The heads are left and right? I don't recall that one and I have plenty of 3900 heads here. What is the casting number difference?

[Joseph Upson]

The heads are left and right? I don't recall that one and I have plenty of 3900 heads here. What is the casting number difference?

Having coolant flow outlets at one end makes them left and right and I distinctly remember the deck surface flow pattern varrying from one end to the other apparently to assist in proper cooling for the u-flow coolant design.

I'm not able to get numbers right now but GM does seem to show more than one part number for various parts in which case this may also explain why two different connecting rod lengths have been measured; 5.827" and 5.9".

[SappySE107]

I have 6 heads with the same casting number 12590746.

[Joseph Upson]

I have 6 heads with the same casting number 12590746.

GM Parts direct listed different prices for the same parts for the 3.5 and 3.9 engines based on production year before rearranging the site. If you go their now you should find at least 3 different prices for the cylinder head between 2006-2007 ranging from ~$ 134, 178 and over 200 by the 07 year using different vehicle applications for the same engine, 06 G6 vs 07 Uplander, I have both, and the 07 Malibu Maxx. I also noted two different connecting rod prices. Whether something is added or excluded part wise I don't know.

I had this issue with a set of 3500 heads that I'm certain I'm correct about regarding there being two castings. I noted the difference in the combustion chamber of my cylinder head vs what was posted here on the forum and was also asked by a parts supplier upon looking for a set "Which casting number do you have".

Recall there are also two crank castings one of which you don't see much of anymore and that being the cast iron crank. When I return home shortly I'll take pictures of it but I'm sure my eyes did not deceive me in noting the difference in the cylinder head coolant passages from one end to the other.

[SappySE107]

I can't tell you what GMPD is doing for pricing, but the only 60V6 to use left and right heads are the 3.6 DOHC. There could be different casting numbers, like the 170 and 487 for 3400, but they are identical minus the newer 487s got 8mm rocker stud bosses.

The 3900 heads have holes on both ends for the coolant to go, and the other side of the head uses a gasket to seal it off.

[gectek]

wrong...same part number...12594246...same number on AFM, Flex fuel and regular, with or without the tunable upper

[Joseph Upson]

I can't tell you what GMPD is doing for pricing, but the only 60V6 to use left and right heads are the 3.6 DOHC. There could be different casting numbers, like the 170 and 487 for 3400, but they are identical minus the newer 487s got 8mm rocker stud bosses.
The 3900 heads have holes on both ends for the coolant to go, and the other side of the head uses a gasket to seal it off.

I know the heads can be turned around and that the rear of the head has a freeze plug in the hole that serves as a water outlet on the other end, but for someone who knows nothing about the engine and is considering a swap the point has to be made that turning a head around on the 3900 is not a simple process and if you fail to specify which head you're ordering you can wind up having to remove and install a freeze plug, I'm pretty sure about the assemetry of the coolant passages.

wrong...same part number...12594246...same number on AFM, Flex fuel and regular, with or without the tunable upper

If you're talking about the VVT 3500 you're on a different page, I'm refering to an old thread on the non VVT 3500. Same part number or not the combustion chameber in my 3500 cylinder heads was different than what was posted here and not being able to find a different part number doesn't change that.

No one has been able to explain the 5.827" connecting rod in an engine advertised as having 5.9" rods, and a couple of years back when I was being told my 3500 engine did not have a steel crank in it because GM said it was only installed in the 3900 found in one of the 06 sport utility vehicles, I wound up proving they had been installing the steel crank in the first year 3500 as both my 04 and 05 engines had it.

Assuming not because there are no part numbers to support what I'm telling you is a gamble. I'm telling you guys what I saw clearly with my own eyes.

If I find I'm mistaken the next time I examine the heads I will post a correction.

[gectek]

i thought this thread was about the 3900 i was talking about the 3900...the 3500 non vvt and the heads have the same pn also...but you are right...there is a coolant temp sensor, but idk how they actually come...ive ordered them in, but i havent looked at them, lol

[Joseph Upson]

i thought this thread was about the 3900 i was talking about the 3900...the 3500 non vvt and the heads have the same pn also...but you are right...there is a coolant temp sensor, but idk how they actually come...ive ordered them in, but i havent looked at them, lol

Coolant sensor shouldn't be a problem as I can see a hole in what appears to be the same location on the front of the aft cylinder head. There is a cutoff date showing up on GM Parts direct, I was on the wrong GM site which showed some different prices. The direct site is showing the same price for both heads but an 06 and 06-07 distribution. I would really like to get to the bottom of the connecting rod length differences that have come up which show the same kind of cutoff date.

Something has to be different between these engines and there's no telling how close they are to documented specs. Two different rod lenghts have to be corrected for by either a piston change or crankshaft change.

Speaking of which, the 05-06 crankshaft is more expensive than the 07 crankshaft, I don't believe it's safe to swap anything across years as far as the rotating assembly with these engines, especially since when ordering parts the VIN number is almost a requirement. I distinctly remember the 3900 crank looking a little bit more trim than my 3500 crank and I'm almost positive I wrote that in a thread some time ago. It maybe heavier or possibly stronger from additional processing that is no longer being performed.

http://www.gmpartsdirect.com/catalog/frameset.cfm

[SappySE107]

There are no freezeplugs on my 3900 heads, nor is there any proof that there are left and right heads. There is proof that there are not, and I am looking at them.

[Joseph Upson]

There are no freezeplugs on my 3900 heads, nor is there any proof that there are left and right heads. There is proof that there are not, and I am looking at them.

In all likelyhood your heads are different than mine. There is a cap at the back end of both of my heads that I call a freeze plug because it's made of metal and that's what it looks like.

If you swap the heads around leaving everything else the same and bolt everything back in place, water will poor out the back of the cylinderhead and there will be no return coolant flow from the front and that's why I address them as left and right.

Some others address them as front and rear all because of a technicallity that prevents them from being bolted on either side of the engine without making a modification, that being removing the freeze plug, coolant outlet cap "thingy" (whatever you want to call it) from one end of the head and placing it at the other if you want to move the head from one bank to the other and have the system function normally.

You may not think much of it, but I like to know details like this. As for the deck surface, I should have taken pictures when I thought to do so upon seeing the unusual pattern, understand I'm referencing from one end of the cylinder head to the other end of the cylinder head on the same cylinder head, in other words folding the surface in half does not produce a mirror image.

I'm talking about the plugged holes in the back of the heads posted in the pictures for others who may be wondering.

[gectek]

those are on an assembled engine. they will look like that, but you have to use the plugs so that everything works right

and as long as the ports on either the block deck or the cyl head deck are large enough...shape doesnt matter